As the stage version of The Sagas of Noggin the Nog heads to Edinburgh, artist Peter Firmin shares the unlikely inspiration for the lovable Norse prince and explains why new generations still fall under his spell

Peter Firmin is trying to remember how he came up with the name Noggin the Nog. "Going on the tube to north London, because the TV studios were up there, I remember seeing Neasden and thinking: Noggin." He breaks off and, from the sofa in the library of his home in Kent, scans a nearby bookshelf as if looking for answers. "There was a company that produced artists' materials, and it was called Nog something. I thought, that's quite a good prefix, Nog. They'll be the Nogs. And there'd be Nogbad and Thor Nogson."

First broadcast on the BBC in 1959, Noggin the Nog related the adventures of a mild-mannered Viking prince, setting sail across the cold seas to find a bride before his evil uncle, Nogbad the Bad, comes to claim the throne for himself. Firmin, now 85, recalls that his children also helped him him to name his animated cast. As a toddler, his daughter, Hannah, had seen the film Nanook of the North, in which Inuit characters slept naked under sealskins. She said to him one night: "I want to go to bed with nothing on and be a little nook." And so Nooka of the Nooks was christened. "That's how these things come along – from all sorts of directions," says Firmin, turning his head to listen to his Jack Russell, Tiny Tim, howling at a passing ambulance. "He thinks it's the wolf pack," he says with a smile.

In the garden is the barn where, more than half a century ago, Smallfilms was founded. It was here that Firmin and his late counterpart Oliver Postgate came up with their peculiar, affectionate animations starring knitted aliens, saggy cloth cats and polite little Vikings. Even today, new generations are still falling under the spell cast by The Clangers, Bagpuss and Noggin. At this year's Edinburgh festival, a small theatre company is even staging its own version of The Sagas of Noggin the Nog, perhaps Postgate and Firmin's most melancholy children's series.

How has this 55-year-old black-and-white cardboard animation (two stories were remade in colour in the 1980s) so outlived the natural lifespan of a children's TV show? Such programmes are meant to be ephemeral fun, something that perhaps stirs a little shiver when you hear the theme song years later. Yet Noggin, Bagpuss, the Clangers and their Smallfilms stablemates – all shot in outbuildings in Firmin's garden – are still eagerly sought out, discussed with love, watched on DVD and enthusiastically passed down the generations.

Anthony Gleave, an actor and a director with Third Party, the company behind the stage show, says there was only one contender when they decided to make a piece of family theatre. He headed to Kent to plead for the rights from Firmin and Daniel Postgate, Oliver's son. "I was four when I first saw Noggin and heard its strange, fascinating opening music," Gleave says. "It stayed with me. Noggin is a classic."

John Wright, who will direct the new show, singles out the incongruity of friendly Vikings. "It's so English, not Norse at all. And so polite, in that old-fashioned way." In Third Party's interpretation, the story of the Nogs is told by a group of rough-hewn Viking clowns who use puppets and draw the younger audience members in with a bit of traditional interaction. However, as Firmin recalls with a smile, when they first saw the play performed in Ramsgate, the audience was largely made up of "hairy old men".

Peter Firmin: 'If a child can see how something on-screen is done they think, "Oh I can do that."'

Although Postgate is often talked about as the creator of the programmes – largely because it's his voice you can hear – Smallfilms sprang from the combination of two beautifully matched sensibilities: Postgate's passion and drive running the machinery, Firmin's artistry and imagination fuelling the creative boiler. Firmin, who still works as an illustrator and artist from that same barn, says: "I can do a lot of things, but there's a limitation. I always relied upon Oliver. He was very good technically. He could sell things to people. I wouldn't have done all that on my own. I think partnerships really are the thing."

But Noggin was Firmin's brainchild: the idea came to him when he saw the Lewis chessmen in the British Museum. These curious little ivory figures, found on a Hebridean beach around the 1830s, are a favourite of visitors, their odd, comical expressions belying their mysterious origins. They were possibly the cargo of a 12th-century merchant from Norway, but no one knows for sure. The queens sulk on their thrones, leaning their chins forlornly on their hands. The glowering knights chew on their shield edges as though they were ship's biscuits. The chessmen appealed to Firmin's sense of fun and his love of Norse legend. "I come from Harwich, in Essex, and I had an uncle in Denmark," he says. "And I'd been there with a youth party just after the war. I just fancied the Viking sagas, because a lot of them are connected with the east coast of England."

As the TV series progressed, the romance between Noggin and Nooka gave way to more magical elements, with dragons and giants roaming the hillsides. Ever self-effacing, Firmin says this was Postgate giving the stories "their sparkle" and a Tolkien-like quality he didn't originally have in mind. "Oliver never wrote love stories," he says, looking out of the window. "If you think of all the things Oliver did – the females are always rather unsatisfied women who want new hats, or want to be taken out. But there's never any romantic story there."

Married for more than 60 years to his art school sweetheart Joan, with six daughters and a gaggle of grandchildren, Firmin seems well-disposed to the world. This warmth is evident in Noggin. As well as curating exhibitions of his puppets (including Basil Brush – yes, he also designed and made him), Firmin is now working with Daniel on the BBC remake of The Clangers. They're pleased with the early results. Despite Firmin's admiration for the capabilities of modern computer animation, he thinks the charm and appeal of those early Noggin tales lay in their apparent simplicity. "If a child can see how something on-screen is done, with bits of cardboard and shadows, they think, 'Oh I can do that.'" He was relieved to see that the new CGI Clangers really do look like knitted toys come to life. The magic is intact as far as he's concerned.

Nogbad the Bad … the Lewis chessmen at the British Museum inspired Noggin and the eventual cast of cardboard characters

Firmin talks with similar childlike enthusiasm about the Noggin stage show: "When we saw it, we were delighted because it's a bit silly." He often uses the word silly in an entirely positive context. "I think the show appeals to all ages really, to people who remember the series and children who've never seen it." Later, as we look round the barn, he says: "Of course, I'm Thor Nogson." He grins, points to a golden Viking helmet balancing on a rafter, and tells me about the time he dressed up as the character in full cloak, helmet and dagger to host an event during the York Viking festival, which culminated in him leading a band of roaring children through the city streets, a smile on his face as wide as a longboat.

The magic of Smallfilms didn't die with Postgate in 2008 – it has been carefully guarded by his collaborator and friend. Firmin's eyes wander back to the garden where Tiny Tim is chasing a bee. "In a way," he says, "neither of us really grew up."